Advancing age and the male gender are risk factors for cardiovascular disease and are associated with vascular endothelium dysfunction. While the molecular mechanism mediating endothelial dysfunction has yet to be fully elucidated, it has been suggested to involve a decrease in nitric oxide (NO) bioavailability. A decline in NO may be due to (1) alterations in the activity/expression of the enzyme endothelial NO synthase (NOS 3), (2) alteration in NOS 3 substrate/cofactor availability, or (3) increased degradation of NO by superoxide. The rationale for this proposal is that a gender difference in the effects of age on NOS 3 regulation and NO bioavailability may contribute to the gender difference in endothelial dysfunction. The goal of this proposal is to examine how advancing age alters the NOS 3 system and oxidative stress in male and female rats. We hypothesize that with age there are alterations in NOS 3 regulation and increased oxidative stress resulting in decreased NO. In addition, we hypothesize that females will be "protected" from these effects of aging, such that males will experience a greater decline in NO compared to females. The aims of this proposal are to (1) test the hypothesis that male and female rats differentially regulate NOS 3 with advancing age, and (2) test the hypothesis that indicators of increased oxidative stress with age will appear in male rats at an earlier age compared to females. To address the first aim we will examine endothelium-dependent vasodilation and NO bioavailability in resistance-sized arteries from aging male and female rats. We will examine how NOS 3 regulation is altered with age, and if the effects are gender-specific. To address the second aim we will examine indicators of oxidative stress in male and female rats over a progression of ages. We will then determine the affects of age and gender on antioxidant systems and the sources of oxidative stress in the mesenteric vasculature.